[Boatanchors] [ARC5] Taylor Super Modulation and RothmanModulation

[Richard Knoppow]

----- Original Message ----- 
From: "mac" <w7qho at aol.com>
To: "Henry Mei'l's" <meils at get2net.dk>
Cc: <boatanchors at mailman.qth.net>; <arc5 at mailman.qth.net>; 
<milsurplus at mailman.qth.net>
Sent: Wednesday, February 02, 2011 7:59 PM
Subject: Re: [Boatanchors] [ARC5] Taylor Super Modulation 
and RothmanModulation


> Rothman modulation is/was one of several carrier control, 
> screen grid
> modulation schemes.  Some wild claims made for it as I 
> remember but,
> in actual fact, nothing particularly remarkable about it.
>
> Taylor "Supermodulation" was a scheme for using a pair of 
> grid
> modulated tubes coupled together in a novel way so as to 
> achieve
> results equivalent to high level plate modulation but 
> without the high
> powered audio components.  Besides the obvious savings in 
> component
> costs and power efficiencies Taylor also made such (wild) 
> claims as a
> greater ratio of sideband to carrier power and reduced 
> bandwidths
> comparable to those achieved by SSB systems.  For the 
> definitive
> analysis and critique of the Taylor system and it's 
> claimed benefits
> see QST, December 1950, page 33 "Supermodulation" - An 
> Evaluation and
> Explanation by Oswald G. Villard, Jr.  W6QYT.  Villard, 
> BTW, was a
> professor in the Stanford University Electrical 
> Engineering Department.
>
> Other articles:
> Radio News, Sept. 1948, June 1949, Feb. 1950, May 1950 & 
> July 1950.
> Also,  U. S.  Patent #2,282, 347
> Other stuff in CQ and Electric Radio as well.
>
> Dennis D. W7QHO
> Glendale, CA
>
    Thank you so much for the citation. I was able to 
download the article from the ARRL web site, I also 
downloaded Taylor's patent from Google Patents. It will take 
some reading but I think I have an elementary understanding 
of it.
     There have been many schemes to increase the efficiency 
of AM transmitters employing low-level modulation, the 
Dougherty amplifier is perhaps the best known one. There 
have also been numerous schemes to increase average 
modulation level; the simplest is peak clipping but that 
results in gross distortion if much is used. Other schemes 
have involved phase flippers to take advantage of the 
unsymmetrical characteristic of the human voice. These date 
back to simply connecting the microphone so that positive 
pressure on the diaphragm results in upward modulation. CBS 
Labs used a flipper in the Audimax (or was it the Volumax?), 
a pair of awful-sounding processors, CBS was good at self 
dilusion. All really result in upward overmodulation, a sort 
of mild carrier reduced DSB. As the QST article points out 
all these schemes result in increased distortion.
    Most modern broadcast transmitters use either a 
modification of the Dougherty system (Continental 
Electronics) or pulse-modulation. The latter is capable of 
very high plate efficiency with low envelope distortion. 
Weldon's version of the Dougherty amp has substantially 
lower distortion and much better stability but still 
requires two phase shift networks. Both of these schemes 
have the advantage over plate modulation of eliminating the 
modulation transformer, an expensive device and difficult to 
make if the fidelity is to be good. Both also are capable of 
continuous full modulation, assuming the power supply is 
adequate. The latter is valuable for modern broadcast use 
where extreme amounts of processing are used.
     BTW, is there anyone else here who remembers when AM 
broadcasting stations actually emitted high fidelity audio?


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com